Asbestos air testing

Last Edited By Krjb Donovan
Last Updated: Mar 13, 2014 03:06 PM GMT



I have a specific question about PCM and TEM, but let me give you some background information first.
 We are having a bathroom addition put in this spring and builders ran into a small amount of old pipe insulation containing asbestos. The three foot piece of insulation later fell into the crawl space under the new bathroom! I saw it all broken up and disintergrated in the crawl space. I called the EPA and they recommended I cover it up with a wet towel, which I did. THe next day the contractor "cleaned it up" but I'm not sure how well it was done. Since I am paranoid b/c I have two very small kids at home living us, and the crawlspace was continuous with my basement, new bathroom, and kitchen, I called in a environemental air testing service to come in and test the air for asbestos levels. He ordered PCM and I got 5 readings, the highest were all within closer proximity to the accident. The values were (fibers/ml) 0.007, 0.005, 0.005, 0.005, 0.003. I know the OSHA cut off is less than 0.01 but now I am reading on the web that TEM is really the best test b/c it can detect much smaller and thinner fibers and PCM does not distinguish between other types of fibers. It was tested at a very reputable lab over the span of 2 hours with 1200 liters of air. However, do you think I should retest possible contamination sites again with TEM even though it costs more $$$, perhaps it will give me a better idea of how much asbestos I am really dealing with. I have read alot about these types of testing in the internet and would appreciate any advice. I really just want to keep my home enviroment as safe as possible for my children since they spend alot of time at home.

thank you.

ANSWER: It sounds as if you have done your due diligence to assess the situation, and the results are definitely acceptable. You should not have reason to worry at this point. Let me explain why.

First of all, 3 lf of pipe insulation is an extremely small quantity. For example, the EPA does not even care about projects involving less than 260 lf of pipe insulation. They have no reporting or disposal requirements for projects under this size, because they consider it such a small quantity. In many parts of the country where the EPA demolition laws are the most stringent overriding law, your neighbor could knock down their house with this amount of asbestos in it, and the EPA would be perfectly fine with it.

In higher density urban areas, many counties or states have stricter laws. For example, in Illinois, the state health department regulates asbestos quantities in commercial and public buildings, and sets is minimum threshold value at 3 linear feet of piping. Anything less than that, they say is insignificant.

So, the first thing you have going for you is the extremely small quantity of material that was disturbed.

The main thing that matters is that it was cleaned up. As long as the material was physically removed, then your source of fibers from a deteriorated material has been eliminated.

Whenever calls like yours come in to the consulting company I work for, the recommendation is to simply wet down the material, and bag it up and dispose of it. We would typically not even recommend any additional air testing because it really is such a small amount of material they would be highly unlikely to result in a significant exposure scenario just from a single disturbance episode. Nontheless, many homeowners do still opt to proceed with air testing as you did, for peace of mind purposes.

With regards to selecting PCM vs. TEM, you are correct about the increased analytical sensitivity of TEM. This is a benefit, but it is not the main difference. The big difference is this:

PCM counts ALL FIBERS. It can not differentiate between an asbestos fiber, a cotton fiber, a fiberglass fiber, a carpet fiber, a wood fiber, etc, etc. It is simply counting visible fibers that were collected on the air filter cassette. The analysis ASSUMES that all fibers as asbestos, yet in realilty this is not true. PCM reports result in fibers per cubic centimeter of air (1 cc = 1 ml). The results are basically in units of fibers per VOLUME of air. The acceptable level of exposure to asbestos, according to OSHA, is 0.1 f/cc, over an 8-hour working day, for an entire working lifetime. The CLEARANCE level, demonstrating acceptable cleanup following an abatement project is 1/10th that level, at 0.01 f/cc. This low level approaches the analytical sensitivity of the PCM method.

TEM has the captility to identify a fiber, and then look at the elemental composition of the fiber as well. If the elemental composion matches one of the 6 types of regulated asbestos minerals, then it is reported as an asbestos fiber. Therefore, TEM results are truly the actual count of asbestos fibers. TEM results are reported differently than PCM. They are reported in units of fibers per square millimeter on the filter (f/mm2). In otherwords, they are reported in fibers per area of filter, vs. PCM which reports fibers per volume of air drawn across the filter. This creates a lot of confusion when homeowners try to compare the results between PCM and TEM. They are not directly comparable. The clearance limit by the TEM method is 70 asbestos fibers (asbestos structures) per square millimeter, usually written S/mm2. If the result is <70 S/mm2, you pass.

If you want to compare the TEM results to PCM, you can ask the lab to calculate the PCM-equivelant (or PCM-e), which will then report the TEM result in S/mm2, and also f/cc. Not all labs provide this PCM-e result on their standard report format, and you will have to ask for it. This PCM-e result, in f/cc, is then the TRUE concentration, of actual asbestos fibers in a volume of air.

At my employer, we often do side by side TEM and PCM for supporting litigation cases. We have a "test chamber" (think of it as an isolated bubble room), where we conduct experiments working with asbestos products to determine what an exposure would be to using the product under certain work conditions. We collect many simultaneous samples, by both PCM and TEM, and compare the results by the 2 methods. In general, there is a good correlation, and what we find is that the PCM does over estimate the actual amount of asbestos, because once again, it is counting ALL fibers, not just asbestos fibers. The side-by-side TEM result with the PCM-equivelant will typically show that the true asbestos-fiber count is even lower than the PCM assumed.

So, if you are still follwing me here, sorry to be so technical but I have to be to explain what you are asking....

The POINT IS - if the PCM results pass - you are FINE! 5 samples is a good representative group of samples for such a small quantity release. 1200L of air is a very appropriate sample volume. You should put your mind at ease that you did the tests, and the results indicate that everything is well within the acceptable range. You are beneath the clearance limit, and you are less than 1/10th of the OSHA permissible exposure limit (PEL). If you were to proceed with additional TEM tests, it would be costly obviously, and I am certain that you would not find any results significantly different from what you already know from the PCM.

Good for you for taking the effort and spending the money to assess the concern. The results look fine. Relax!

---------- FOLLOW-UP ----------

QUESTION: Because I am an OCD mother of two small kids, this whole possibility of traces of asbestos in my basement and crawlspace still concerns me and so I am seeking your advice again.

I have been considering either 1)hiring an asbestos abatement company to do a proper clean up of my basement and crawlspace with wet down cleaning and negative air pumping or 2)just getting a good clean out from a post-construction cleaning service and then air out my house.

The main concern I have is that I cannot get a good air flow to remove whatever asbestos may remain in my basement b/c my basement only has one tiny window, so there is little way to get good air circulation. I have even looked into purchasing a negative air pressure pump to do this ourselves, but it doesn't seem like they are not easy for the general public to purchase.

Do you think it's worth getting the abatement company to do the work or do you think they really aren't going to help my situation? Money is not the issue here, I just want to get the best result.

thanks again in advance.

ANSWER: If money is not an object and you feel that this is necessary to give you peace of mind, then here is what I would recommend.

Hire the asbestos abatement company for sure over a general contractor because the abatement contractor will be familiar with proper work practices for asbestos. A contractor would obviously know how to "clean up" regular dust, but similar practices could actually worsen a situation with settled asbestos dust. Disturbing settled asbestos dust by dry sweeping, brooming, vacuuming with a regular vacuum, etc., can re-aersolize the asbestos fibers and worsen the situation. An abatement contractor will know to use only HEPA vacuums, only wet-wipe, never dry sweep, etc. Also, an abatement contractor will know how to properly set up the basement for proper directional airflow with the neg-air machine.

You are right, neg-air machines (NAMs) are not meant for the average consumer purchase. They are $1,000+ for a good 2000 CFM machine w/ HEPA filter, and very bulky and heavy.

For cleanup of surfaces which "may" be contaminated with asbestos dust, here is what I recommend.

1. Isolate the area of concern. The abatement contractor should put up polyethylene plastic sheeting over doors and openings to other areas of the house. This will isolate the "contaminated" area during cleanup and prevent fiber migration into unaffected parts of the house. The poly barriers should be duct taped at the seams and air tight. The contactor will need one doorway to enter/exit the work area. Over this door, hang 3 sheets of plastic, with offset vertical slits for the men to wiggle through into the work area (this is called a "Z"-flap, because the offsets of the slits in the plastic form a "Z" shape.

2. Shutdown any ventilation system serving the "contaminated" area (if one exists). Also, place poly sheeting over the supply and return vents (if they exist) to seal those off.

3. Setup the negative air machine. The machine should be placed as far away from the entrance to the work area as possible (away from the Z-flap entrance). This causes a good cross-draft. Clean air from the house gets pulled in through the Z-flap, traverses the work area, and then exits the basement by getting sucked into the NAM, being filtered through the HEPA filter, and then discharged out of the house through a window (basement window well if you have one). A little simple math is involved in figuring out what size NAM you need (the Cubic Feet of air per Minute, or CFM rating, or "R" in the equation below). You want it sized to get AT LEAST 4-air changes per hour. First, calculate the volume (V) of the basement and crawl (widthxlengthxheight). The number of negative air machines you need (#) is found by the following equation: #= 4V/(60R). Whatever # calculates out to be, round up to the next nearest whole number, and that is how many NAM's you need to get at least 4-airchanges per hour in your basement. My guess, is it will be just one 2000 CFM machine, unless you have a large basement.

4. Once the work area is isolated and under negative pressure, it's time to clean. The protocol should be only wet-wiping and HEPA-vaccuming of all horizontal surfaces where dust may have settled. After they are done cleaning, the rooms should be able to pass a "white-glove test". Meaning, if you were to put a white glove on your hand, and rub it over any surface in the room, the white glove should still be clean.

5. Don't be surprised if the abatement contactor will require you to have another air clearance test performed after they are done cleaning. This is often required by their insurance carrier after ANY job to prove that they are leaving a site clean and help refute any future potential liability claims.

---------- FOLLOW-UP ----------

QUESTION: How reliable are the PCM results if they were done in an area that has little air current (crawl space and basement)? We did not have air fans blowing while the air pumps were colecting samples. Thanks for your advice and experience.


PCM samples (or any type of air sample for that matter) can be collected 2 different ways, static or aggressive.

Static sampling is when you collect the air samples in a room without agitating or stirring up the air beyond what is normally present due to building ventilation and air currents.

Aggressive sampling involves agitating the air to create a "worst-case scenario" and re-suspend any asbestos fibers that may have settled out into dust on the floor back into the air so that they show up on the air sampling cassettes.

Following an asbestos abatement project, air-clearance testing is supposed to be done by agressive means. This is required by law for asbestos air clearance testing in schools. It is considered "best-practices" for other non-school air clearance projects. The key thing to remember here is that clearances done after an abatement project are done while the containment barriers (plastic sheeting) is still in place. Therefore, by resuspending any remaining asbestos fibers back into the air, IF the containment fails to pass clearance, you have not worsened the situation and contaminated other parts of the building because the work area is still contained. You just go back in, reclean by HEPA-vaccuming, wet-wiping, and running negative air machines, and then re-test again using aggressive methods. There is actually a protocol stating how to "aggressively" agitate the air. You are supposed to start by using a leaf blower and direct the exhausted air against walls, ceiling, floors, ledges, and other surfaces in the room for at least 5 minutes per 1000 sq ft of floor space. This will resuspend any settled asbestos fibers back into the air. Then, 20-inch fans are to be used for air circulation for the duration of the air sampling procedure to keep the fibers suspended in the air. The fans are to be operated at the lowest speed setting, placed in the center of each room where sampling will take place, and at least 1 fan per 10,000 cubic feet of room space shall be used. If the samples pass the clearance criteria following an aggresive sampling procedure, you can be assured that the area is truly clean, and that it didn't just pass because all of the fibers settled out of the air, but could be redisturbed and cause a problem later on.

While aggressive sampling methods are preffered over static, they are not always appropriate. One example where static is preferred is when responding to a disturbance episode, following cleanup. This is because, if a containment is not in place, you risk spreading contamination by leaf-blowing and using fans. In this case, a static air clearance is the safest practice, while still providing useful data.

In your case, if you wanted to do an aggressive clearance, first you would have to remove all contents from the basement and crawl. Treat them as contaminated before relocating them to another area, so wet-wipe and HEPA-vac them before moving them to remove any potential asbestos fibers settled onto the contents. Once the basement/crawl are totally clear, then isolate these areas by erecting plastic sheeting and shutting down any HVAC serving the spaces. Place the area under negative presure using negative air machines. Then conduct the aggressive sampling. Another factor to consider is what the floor of your crawlspace consists of. If it is a dirt or gravel crawl, you will never be able to read the samples because the leaf-blower and fans will kick up so much dirt/gravel dust into the air that it will obscure the samples and render them impossible to analyze. If you have a concrete floor in the crawl, then you would be ok, just clean it well first. If you have a dirt/gravel floor in the crawl, this would be another instance where static sampling would be the preferred method.


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